In the Garden:Upper South
October, 2006
Regional Report

The combination of alliums 'Purple Sensation' and 'Globemaster' with 'Amazone' phlomis is a study of textures and forms.

Show-Stopping Onions

Perhaps you've looked at the photos of the large ornamental onions on the bulb packages or in the catalogs and wondered if they were for real. And surely the description is just so much catalog hyperbole? Fortunately, this is one of those times when you can really believe what you read. Distant cousins of garlic, these alliums are sometimes called ornamental garlic or flowering onion. While these names convey the allium's bulbous nature and familial scent, they fall short in communicating the exuberant good looks of this sophisticated plant group.

Although there are several hundred species of allium, only several dozen are grown in gardens. Best known are the taller alliums, with their long, sturdy, 2- to 3-foot-tall stems and signature dense puffball-like heads of purple flowers, which can range from 4 to 12 inches across. These taller alliums excel in the garden as elegant vertical accents with architectural interest. 'Globemaster' and 'Purple Sensation' are two popular varieties. For an allium that resembles lavender-blue fireworks, try Allium albopilosum, also known as Allium christophii or Star of Persia.

There are also lesser known, more subtle alliums. These low-growing bulbs reach only 8 to 14 inches tall and have widely varied forms and flowers. Where purplish shades dominate among the larger types, the low growers sport flowers of white, yellow, pink, lavender, or ivory.

Ornamental alliums grow best in well-drained soil but they survive in a wide range of soils. Choose a spot with full sun or light shade. Plant at a depth twice the diameter of the bulb, in loose clusters of five, seven, or more and spaced generously, as most will perennialize to form large and beautiful clumps over time. Alliums are the last of the spring-flowering bulbs to bloom, usually from May through July. They make great cut flowers, and the large-flowered types dry beautifully.

Perennial Partners
Alliums are great for adding drama to perennial plantings. The Dutch landscape designer Piet Oudolf has developed some inspired combinations at the Battery in New York and Lurie Garden in Chicago's Millenium Park. The combinations demonstrate season-spanning plant partnerships that bring ebbs and flows of interest over a long period. Oudolf's forte is selecting individually interesting plants that, when planted together, surprise and delight via their interplay of foliage, form, and flower color, with height, texture, movement, bloom, and after-bloom aspects taken into account.

2. Allium cowanii + hosta 'Maraschino Cherry'. A charmingly quiet combination, with the broad, shiny, dark green leaves of the hosta creating a soothing backdrop for the loose clusters of glistening white star-shaped florets that bloom for a long period in early summer.

3. Allium karataviense 'Ivory Queen' + Sporobolus heterolepsis. Elegant, low-growing 'Ivory Queen' has broad, lush, blue-green foliage and 3-inch balls of ivory florets in May and June. The dense solidity of the allium is set off by the sleek drape and airiness of the low-growing native ornamental grass also known as prairie dropseed.

3. Allium christophii + Sporobolus heterolepsis. This combination gives a completely different look as both the allium and ornamental grass have an airy effect. Let the dried allium flowers drape over the grass, and leave them both in the garden through winter.

4. Allium christophii + Sporobolus heterolepsis + Eryngium yuccifolium. What was spectacular becomes awesome with the addition of the towering native perennial rattlesnake master added to the mix. Growing up to 5 feet tall with yucca-like foliage and nubby round white flowers, the eryngium takes the combination in a completely different direction. Now there are airy architectural allium umbels set against the wispy grass foliage and the stiff, spiky, flat leaves of the eryngium.

5. Allium 'Purple Sensation' + heuchera 'Caramel' + Gillenia trifoliata. 'Purple Sensation' introduces an upright spherical element to the lower growing heuchera and bushy Bowman's root, another native perennial. 'Caramel' has leaves that are golden in spring, becoming more apricot as the season warms. Bowman's root has mahogany stems early in the year, followed by white flowers from early summer through autumn, and reddish fall foliage.

6. Allium 'Purple Sensation' + Geranium phaeum 'Springtime'. In this pairing, the excitement comes from color play and contrast of shape. Tall, sturdy spheres of reddish purple contrast against the low-growing, softly curving geranium with its maroon flowers. Other delightful partners for 'Purple Sensation' include Deschampsia cespitosa 'Goldstau' or 'Goldstein' (tufted hairgrass) and the hardy Gladiolus communis byzantinus, with its small, fragrant cerise flowers.